a) Field of the Invention
The invention relates to an arrangement for the detection of illumination radiation in a laser scanning microscope.
b) Description of the Related Art In DE 197 02 753, a portion of the excitation output is deflected to a monitor diode in a laser scanning microscope in the excitation beam path in front of the main color splitter by means of an additional reflecting arrangement.
The arrangement for reflection onto the monitor diode can accordingly be arranged in the beam path in such a way that the laser light strikes the coating or layer in a p-polarized manner while the main color splitter is struck with s-polarization.
The light exiting from the light-conducting fiber is linearly polarized at better than 100:1. This is achieved by stress-induced birefringence. In a corresponding manner, the linearly polarized laser light can be guided in the fiber in two axes perpendicular to one another. Derived from this degree of polarization, the electric field strength vector has an x-component and a y-component (s-pole and p-pole) with an intensity ratio of 100:1. In order to achieve this degree of polarization at the fiber output, it is necessary to couple in the linearly polarized laser light parallel to one of the birefringent axes of the fiber. The orientation of the birefringent axes can vary by fractions of angular degrees relative to the polarization direction of the laser due to environmental influences. The portion of laser light that is coupled into the respective axes can vary in a corresponding manner. With respect to the polarization at the fiber output, this means that the intensity ratio between the x- and y-components of the electrical field strength vector varies. The dichroic layers used for the beam deflection in the illumination beam path of the LSM preferentially reflect one of the two components of the field strength vector (e.g., the x-component). When a monitor diode is arranged in such a way that, in contrast to the illumination beam path, the y-component is preferentially reflected in the path in which the monitor diode is positioned, there are different intensity variations in the two beam paths.
Further, a loss in illumination energy results from the additional element for reflecting onto the monitor diode.